Gross chromosomal rearrangements (GCRs) have been identified as mutations that underlie many genetic diseases, including cancer. GCRs also result from the increased genome instability seen in many cancers, which may represent a type of mutator phenotype. Inherited cancer susceptibility syndromes have also been identified that result from genetic defects that cause genome instability in model systems, although whether similar defects cause genome instability and drive the development of sporadic cancers is not clear. While DNA metabolism pathways related to genome instability have been intensely studied, a comprehensive understanding of the pathways and mechanisms that prevent genome instability is not available. Understanding these mechanisms and pathways will impact on human health for several reasons: 1) Identifying the genes that suppress GCRs will provide a basis for understanding the origin of genome instability in cancer; and 2) Genome instability has been proposed as a therapeutic target in cancer and understanding the pathways that suppress genome instability will provide a rational basis for the development of new therapeutic approaches. The goal of this proposal is to use Saccharomyces cerevisiae as a model system to identify the genes and pathways that suppress GCRs. Key related goals are to identify the types of chromosomal features and mechanisms that contribute to genome instability and identify human genes in which defects cause genome instability in cancer. The proposed work will build on insights obtained using previously developed quantitative systems for studying the formation of GCRs in S. cerevisiae. The following lines of experimentation will be carried out: 1) Robotic-based genetic analysis of a bioinformatics-derived set of enriched candidate genes as well as hypomorphic alleles of essential genes including high-density genetic genetic interaction analysis will be performed to identify the genetic network that suppress different kinds of GCRs; 2) Genetic studies will be performed to probe the genome for different genomic features that promote GCRs and identify mechanisms that specifically suppress or promote GCRs mediated by these features; 3) The mechanistic features of some of the pathways that suppress GCRs will be investigated, initially focusing on chromatin remodeling and modification factors and the CDC73 gene whose human homologue is a tumor suppressor gene; and 4) Human homologues of the S. cerevisiae GCR suppressing genes will be used to mine available cancer genomics data sets to identify genes in which defects cause genome instability in cancer. These studies will provide a comprehensive picture of the pathways and mechanisms that prevent GCRs and provide insights into the origin of genome instability in cancer.